Pseudosolenia Calcar-avis Research Articles

Mediterranean-like “fall dump” events in the Baltic Sea

In the Mediterranean Sea, organic carbon-rich sapropels have been deposited periodically over the last fifteen million years. Some sapropels are characterized by high contents of the mat-forming, planktonic diatom Pseudosolenia calcar-avis and the planktonic diatom Thalassionema nitzschioides as a result of their mass sinking in autumn (the so-called “fall dump”). The present study shows that fall dump events also occurred in the brackish Baltic Sea around 6300–5800 calibrated years before present (cal yr BP; present = AD 1950). In sediments from the northern Baltic Sea these events are evidenced by high contents of a lipid specific for P. calcar-avis (a C25:2 highly branched isoprenoid alkene) and corroborated by fossil remains of both P. calcar-avis and T. nitzschioides. A biomarker index based on long-chain alkyl diol lipids indicates that mat-forming Proboscia diatoms were also present. High contents of calanoid resting eggs further suggest that the copepod population was stressed being unable to feed on such large diatoms. The fall dump events occurred during a complete stratification of the water column and euxinic conditions, as reflected by the redox-sensitive trace metal uranium, allowing upward diffusion of nutrients and the growth of rhizosolenid mat-forming diatoms in a deep chlorophyll maximum. Synchronous remains of P. calcar-avis in the central Baltic Sea further suggest that these events occurred on a basin-wide scale.

Biological carbon pump in the Black Sea

In the northeastern part of the Black Sea, the biological carbon pump is represented by both organic and carbonate pumps. The organic carbon pump consists of small-cell diatoms (mainly Pseudo-nitzschia pseudodelicatissima) and large-cell diatoms (Pseudosolenia calcar-avis and Proboscia alata). The carbonate pump is represented by only one species of cococcolithophore, Emiliania huxleyi. These species form intense blooms that require characteristic hydrological and hydrochemical conditions. The seasonal dynamics of the biological carbon pump is as follows: organic pump (spring) → carbonate pump (late spring and early summer) → organic pump (summer and autumn). An exception is the long-term dynamics of carbon concentration, and no significant carbon growth trends have been identified. During the intensification of the work of the carbonate pump, partial concentrations of carbon in water, increased relative to the atmosphere, and an increased influence of the organic pump on high partial pressure are released. In late spring and early summer, CO2 is released in the Black Sea, as a result, absorption increases in summer. The carbonate pump arises with a greater arrival at sea.

Phytoplankton Growth Rate and Microzooplankton Grazing under Conditions of Climatic Changes and Anthropogenic Pollution in the Coastal Waters of the Black Sea (Sevastopol Region)

In the coastal waters of the Black Sea near Sevastopol, a gradual temperature elevation and an increase in anthropogenic pressure since the early 2000s have caused significant structural and functional changes in phytoplankton. Currently, there is a significant decrease in the contribution of small diatom species (Skeletonema sp. and Chaetoceros socialis H.S.Lauder as well as coccolithophorids Emiliania huxleyi (Lohmann) W.W.Hay and H.P.Mohler) to the total phytoplankton biomass in these waters. Previously these species caused regular weak blooms. In the warm periods (from May to October), during which the main phytoplankton biomass is formed, large diatom species Pseudosolenia calcar-avis (Schultze) B.G.Sundström, 1986, Proboscia alata (Brightwell) Sundström and dinoflagellates predominate. Therefore, the maximum values of the phytoplankton community’s specific growth rate are about two times lower than in the preceding periods and do not exceed 1.10–1.40 day−1. There was also a decrease observed in the microzooplankton grazing rate, which, during the year, was no higher than 0.70–1.20 day−1. This is primarily conditioned by the increased role of large algae in phytoplankton, which means a decline in nutrition quality for microzooplankton. As a result of the joint influence of nutrition quality and water pollution, the relative share of net primary production consumed by microzooplankton in the warm periods of the year averaged only 32%, which is two times lower than the average values generally accepted for marine ecosystems. This means that the transfer of matter and energy from phytoplankton to higher trophic levels is significantly decreased.

Protoplasmic streaming of chloroplasts enables rapid photoacclimation in large diatoms

Abstract Long-term (2004–2020) studies showed yearly summer/autumn blooms in the NE Black Sea dominated by large (cell volume > 5000 μm3) diatoms (Pseudosolenia calcar-avis and Proboscia alata). This phenomenon is characterized by high (>250 W m−2 photosynthetically active radiation, PAR) insolation, and low phosphorus concentrations (to analytical zero). These diatoms contained >100 chloroplasts per cell, which at low irradiance are evenly distributed throughout the cell. As light increases (to 1000 μmol photons m−2 s−1 PAR), chloroplasts aggregate within 20 min, usually to the center of the cell. In consequence, the light absorption coefficient is decreased by >3 fold. At elevated photon flux density (PFD), P. calcar-avis also shows a “conveyor” of chloroplasts moving from the aggregate to the cell periphery and back. This mechanism enables a continuous fine-tuning of the cells’ ability to absorb light, likely also facilitating photo-damage repair. This rapid photoacclimation mechanism allows large diatoms to minimize photodamage at high PFD and acclimate well to low PFD. We hypothesize that competitive success of large diatoms in conditions of high light gradients is aided by this short-term rapid photoacclimation enhancing growth rate while minimizing chloroplast repair costs, aided by the ability of large cells to accumulate nutrients for chloroplast synthesis.

ОСОБЕННОСТИ РАЗВИТИЯ ФИТОПЛАНКТОНА СРЕДНЕГО КАСПИЯ В ЛЕТНИЙ ПЕРИОД

The article highlights the quantitative and qualitative characteristics of phytoplankton organisms in the water area of the Middle Caspian Sea studied by sections: the city of Makhachkala-cape Sagyndyk, the city of Derbent - cape Sandy, Divichi village - Kenderli bay in 2019-2020. The saprobity index and the corresponding saprobity zone of the studied areas have been determined. It has been found that the dominant group was presented by diatoms (43% of the total com-position). The subdominants were dinophytic algae. The basis of the ecological complex of 2019-2020 was made up of representatives of freshwater groups of algae. Only on the section of Divichi village - Kenderli bay there dominated the species of marine origin. Quantitative indicators of phy-toplankton, both in the Middle Caspian as a whole and by sections, in 2020 decreased compared to the previous year. The general part of the biomass was formed by a large diatom Pseudosolenia calcar-avis and representatives of the group of dinophytic algae. The leading role in the abundance figures of the Middle Caspian in 2020 was played by small-cell phytoplankton, mainly from diatoms - Thalassiosira hustedtii, Thalassionema nitzschioides, Aulacoseira granulate, species of the genus Fragilaria. The highest quantitative indicators of 2020 were noted in the section of the city of Makhachkala-cape Sagyndyk in the productive layer of 0-25 m. In 2019-2020, the saprobiological state of the waters of the Middle Caspian was characterized as moderately polluted

Status of plankton algocenosis in the water area of the port of Tuapse and beyond it in the spring-summer period of 2019

The article presents the research of qualitative structure and quantitative development of phytoplankton in the water area of the port of Tuapse and beyond it in the spring-summer period of 2019. In April 2019, 43 phytoplankton species of 5 divisions were found. In the port area, the mean values of abundance and biomass were of 568 thousand cells·L−1 and 206 mg·m−3, respectively; in the open sea area, the values were 1.5 times higher. In the port area and beyond it, diatoms developed abundantly: 98–99 % of the total phytoplankton abundance and 62–65 % of the biomass. Small-cell species Pseudo-nitzschia spp. and Skeletonema costatum s. l. formed the basis of the abundance; Pseudosolenia calcar-avis, Dactyliosolen fragilissimus, and Chaetoceros affinis formed the basis of the biomass as well. In June 2019, a decrease was recorded in qualitative (13 species from 4 divisions) and quantitative values of phytoplankton development. In the port area, the mean values of planktonic algae abundance and biomass were of 59 thousand cells·L−1 and 81 mg·m−3, respectively; in the open sea area, these values were more than 2 times lower. In the water area of the port, euglenids developed abundantly: % of the phytoplankton abundance and 83 % of the biomass; those were represented by a mesosaprobic species Eutreptia lanowii. Beyond the port of Tuapse, euglenids were not found; in terms of abundance, diatoms predominated (95 %): Skeletonema costatum s. l. and Thalassionema nitzschioides. The following Dinophyta species formed the basis of the phytoplankton biomass (82 %): Ceratium tripos, C. furca, Ensiculifera carinata, Glenodinium paululum, Prorocentrum micans, and Protoperidinium crassipes.

The morphology and phylogeny of the diatom genera Rhizosolenia, Proboscia, Pseudosolenia and Neocalyptrella from Gulf of Thailand and the Andaman Sea, with description of Rhizosolenia loanicola sp. nov., Proboscia siamensis sp. nov. and Probosciales ord. nov.

The marine planktonic diatom genera Rhizosolenia, Proboscia, Pseudosolenia and Neocalyptrella have been studied with emphasis on morphology and phylogeny. Material was collected October 2008—January 2011 at seven localities in the four provinces of the marine coastal waters of Thailand: Rayong, Chonburi, Chumphon and Phuket. Fifty strains were established in culture and used for morphological and phylogenetic analyses, complemented with morphological studies of field material. Morphological studies were done using light microscopy, scanning and transmission electron microscopy. Ten species and two varieties of Rhizosolenia were identified and described in detail: R. styliformis, R. acuminata, R. bergonii, R. clevei var. clevei, R. clevei var. communis, R. formosa, R. hyalina, R. imbricata, R. ostenfeldii, R. aff. pungens, R. setigera and R. loanicola sp. nov. Pseudosolenia calcaravis was also found, and detailed studies indicated that this taxon formed a species complex. Proboscia was represented by P. indica and P. siamensis sp. nov., but more species probably exist. Neocalyptrella was represented by N. robusta. The molecular studies supported Pseudosolenia, Proboscia and Neocalyptrella as separate genera. Culturing and molecular analyses were often difficult or unsuccessful. The data show that Rhizosolenia can be a monophyletic genus if R. pungens and R. setigera, which are distantly related to the remaining Rhizosolenia species, are described as a new genus. This will be done in a companion study of the type material of R. setigera.

CHANGES IN THE DOMINANT SPECIES AND SIZE STRUCTURE OF DIATOMS FROM THE SURFACE BOTTOM SEDIMENTS OF THE SEA OF AZOV OVER THE PAST 20 YEARS

The paper presents the results of diatom analysis of surface bottom sediments selected with a range of 20 years. Samples of surface sediments of the Sea of Azov collected in 1998 (before the salinization period) and in 2019 were studied. The results of the diatom analysis of the bottom sediments showed that the sediments were dominated by spores of diatoms from the genus Chaetoceros and stomatocysts of golden algae. In addition to spores and stomatocysts, diatoms from the genus Thalassiosira sp., Coscinodiscus sp., Ditylum brightwellii, Pseudosolenia calcar-avis and Thalassionema nitzschioides were often found in the surface soils of 1998. In the sediments selected in 2019, medium – and large-sized taxa (Actinoptychus senarius, Actinocyclus octonarius, Thalassiosira sp., Coscinodiscus sp.) began to predominate in frequency of occurrence and abundance. The appearance of these species can be associated with an increase in the average salinity of the waters of the Sea of Azov, since most of the representatives of the above taxa belong to marine and brackish-water-marine species. A decrease in freshwater runoff and an increase in salinity in the Sea of Azov can lead not only to a radical transformation of the native microalgae community, but also increases the risk of alien marine species of plankton and benthos. Large-sized diatoms are less attractive as a food base for zooplankton, which can also lead to changes in the native biota of the Sea of Azov. In general, these dangerous transformations can lead to a sharp decrease in the stability of the ecosystem of the Sea of Azov and irreversible consequences.

Структура угруповання фіто- та зоопланктону шельфових вод північно-західної частини Чорного моря влітку 2019 року

The article presents the results of studies of phyto- and zooplankton of North-Western Black Sea shelf in the summerof 2019. For phytoplankton, 117 taxa from 13 classes were noted, Bacillariophyceae and Dinophyceae dominated.The average abundance was 123 thousand cells*L-1, the average biomass was 713 mg*m-3. Pseudosolenia calcar-avis(Schultze) B.G. Sundstrom, 1986 and Tripos muelleri Bory de Saint-Vincent, 1826. dominated by biomass. The spatialdistribution of chlorophyll-α concentration approximately coincides with the distribution of phytoplankton biomass. Forzooplankton, 30 taxa were noted, the basis of diversity belongs to Copepoda and Cladocera. The average abundance was 10816 ind* m-3, the average biomass was 607 mg* m-3. The genera Acartia, Oithona, Centropages, Penilia avirostrisand various species of the family Podonidae dominated at all the stations. In transitional waters, the contributionof freshwater phytoplankton species to biomass did not exceed 2%, the basis of biomass was formed by marine species.Despite this, in ShW_UA_1 there was a significant negative correlation between biomass and salinity (r = -0.87). Inthe shelf waters of the marine zone, the contribution of freshwater species to the total biomass did not exceed 0.1%,the correlation between salinity and biomass was absent (r = 0.26). At most offshore stations, brackish and freshwaterzooplankton taxa were absent. There was no significant correlation between salinity and zooplankton biomass. As weapproach the estuaries, the biomass of zooplankton decreases with increasing abundance. There is a high negativecorrelation between the ratio of zooplankton abundance to its biomass and the distance to the nearest estuary (r = - 0.90),for phytoplankton this correlation is r = - 0.534. For most offshore stations and horizons, water quality by phytoplanktonindicators can be assessed as GES, by zooplankton indicators, as non-GES.

ОЦЕНКА ФИТОПЛАНКТОНА КАК КОРМОВОЙ БАЗЫ В АКВАТОРИИ СРЕДНЕГО КАСПИЯ

The paper considers the specific features of development of the qualitative composition and ecological groups of plankton algae in the Middle Caspian in the summer of 2019. The yearly dynamics of biomass and the number of algae in the sections of Makhachkala - Cape Sagyn-dyk, Derbent - Cape Peschanny, Divichi - Kenderly Bay has been examined. During the study period 109 samples were collected and examined and 110 taxonomic units of algae were found, with diatoms always prevailing. The structure-forming role belonged to freshwater algae (37 %), which became characteristic of this part of the sea. The biomass and number of phytoplankton in the Middle Caspian made 12.9 million copies/m3 and 166.56 mg/m3, respectively. The layer-by-layer distribution of biomass was determined by the intensity of development of the diatomaceous alga Pseudosolenia calcar-avis. The most favorable conditions for vegetation of dinophytic feed organisms were formed in the western (sections of Makhachkala - Cape Sagyndyk, Derbent - Cape Peschanny) and central (Divichi - Kenderly Bay) parts of the section in a layer of 0-25 m, which presumably has a positive effect on the development of planktonic organisms. Small-cell forms 
 of algae dominated, which is an important aspect in the formation of the fish food reserve.

Medieval versus recent environmental conditions in the Baltic Proper, what was different a thousand years ago?

A sediment record from the western Gotland Basin, northwestern Baltic Proper, covering the last 1200 years, was investigated for past changes in climate and the environment using diatoms as a proxy. The aim is to compare the environmental conditions reconstructed during Medieval times with settings occurring the last century under influence of environmental stressors like eutrophication and climate change. The study core records more marine conditions in the western Gotland Basin surface waters during the Medieval Climate Anomaly (MCA; 950–1250C.E.), with a salinity of at least 8 psu compared to the present 6.5 psu. The higher salinity together with a strong summer-autumn stratification caused by warmer climate resulted in extensive long-lasting diatom blooms of Pseudosolenia calcar-avis, effectively enhancing the vertical export of organic carbon to the sediment and contributing to benthic hypoxia. Accordingly, our data support that a warm and dry climate induced the extensive hypoxic areas in the open Baltic Sea during the MCA. During the Little ice Age (LIA; 1400–1700C.E.), the study core records oxic bottom water conditions, decreasing salinity and less primary production. This was succeeded during the 20th century, about 1940, by environmental changes caused by human-induced eutrophication. Impact of climate change is visible in the diatom composition data starting about 1975C.E. and becoming more pronounced 2000C.E., visible as an increase of taxa that thrived in stratified waters during autumn blooms typically due to climate warming.

ФИТОПЛАНКТОН ОТКРЫТОЙ СЕВЕРО-ВОСТОЧНОЙ ЧАСТИ ЧЕРНОГО МОРЯ В ЗИМНИЙ ПЕРИОД 2017 г.

The seasonal dynamics of phytoplankton development in winter is less studied than in other seasons, therefore it is of certain interest. The article presents the results of the study of taxonomic structure and the level of quantitative development of phytoplankton in the open area of the Black Sea northeastern shelf in December 2017. 34 Species belonging to 5 divisions of Bacillariophyta, Dinophyta, Chrysophyta, Cryptophyta and Chlorophyta were found in phytoplankton. The maximum species diversity was recorded among Dinophyta (21 species) and Bacillariophyta (8 species), other divisions were represented by 1–2 species. Previous studies have shown that the taxonomic composition of phytoplankton in the open area of the Black Sea northeastern part includes a large number of dinophytic species, while the diversity of diatoms is significantly inferior to them. The abundance and biomass of planktonic algae were extremely low during the study period (on average, 2706 cells / liter 11.49 mg / m3 ). The maximum abundance of species (26) and the highest values of quantitative development (5399 cells / l and 32.27 mg / m3 ) were observed in the area of the Taman Peninsula. These values were 2–4 times higher than the values of abundance and biomass found in the rest of the study area. The abundant development of planktonic algae was probably facilitated due to the ingress of waters of the Azov Sea, richer in nutrients, into the Kerch region of the Black Sea. Bacillariophyta (Pseudo-nitzschia pseudodelicatissima, P. seriata, Thalassionema nitzschioides, Pseudosolenia calcar-avis, Ditylum brightwellii), and Dinophyta (Prorocentrum cordatum, Prorocentrum micans and Ceratium species) formed the basis of the abundance (55 and 23 %, respectively) and biomass (24 and 68 %) of phytoplankton. Cryptophyta (Plagioselmis prolonga and P. punctata) accounted for 16 % of the phytoplankton population during the study period. Among the Chrysophyta and Chlorophyta, the species Octactis octonaria and Pterosperma undulatum, common for the open part of the Black Sea, were observed in small quantities. The favorable ecological situation in this region of the sea is proved by the complete absence of Cyanophyta and Euglenophyta, which are indicative of polluted and desalinated sea areas.

Перфорированность панцирей планктонных диатомовых водорослей Pseudosolenia calcar-avis и Proboscia alata (Bacillariophyceae)

Physiological and biophysical characteristics of microalgae should strongly depend on the surface area of the cover of organisms, as all the material-energy streams flow through the surface. However, to determine the relationship between the intensity of the flow of substances with the physiology of unicellular, it is necessary to take into account only the area of perforations, since the rest of the shell is impermeable for substances. The direct determination of the area of perforations on the entire surface of the microalgae is very difficult. Therefore, the indirect method of estimating the perforation area using geometric modeling of the perforation distribution (texture) on the surface was used in this study. The object of the research is two types of marine plankton diatoms with large cylindrical frustules. It was assumed that the frustules are covered with a regular triangular texture of the areola. This texture can be divided into regular hexagons, which allows us to estimate the number of areolas as the ratio of the surface area of the frustules to the area of one hexagon. The model takes into account that each areola is covered with a silicon plate perforated by a smaller pore. The multiplication of the number of areolas on the area of a given pore gives the value of the total area of perforations. Calculations showed that the perforation of the frustules of Proboscia alata was 4%, and Pseudosolenia calcar-avis – 6%. These are the first estimates of the perforation of the entire surface of the diatom frustules. The acquired data confirms the hypothesis that frustules of the most centric diatoms are covered by pores by about 5%, and the other surface is impervious to material flows.

Influence of the phytoplankton community on the hydrochemical structure of the Caspian Sea

The hydrochemical structure of the Caspian Sea, which is formed and changed under the influence of the dynamics of water and the intensity of production and destruction processes, has been studied. The formation of the biogenic base and hydrochemical structure of the waters of the Caspian Sea is greatly influenced by the phytoplankton community. The dominant species of Pseudosolenia calcar-avis and Prorocentrum cordatum, which constitute 60–95% of the population and more than 80% of the total phytoplankton biomass, are mainly responsible for the redistribution of chemical components in the sea.

Drivers of phytoplankton blooms in the northeastern Black Sea

In order to understand of the processes controlling phytoplankton successions in the NE Black Sea, long-term data series are needed. We compiled 15 years (2002–2017) of measurements from which the existence emerges of a tight link between phytoplankton species dominance and nutrients concentrations. The latter is strongly influenced by wind direction. The link between algal dominance and nutrients is mediated by the growth strategy adopted by algal species. In spring, when nutrients are abundant, small diatoms such as Pseudo-nitzschia pseudodelicatissima, with a “rapid growth strategy”, prevail. In late spring and early summer, when N is low and P and Si are high, coccolithophorids such as Emiliania huxhleyi dominate, thanks to an “affinity growth strategy”. Large diatoms, especially Pseudosolenia calcar-avis, dominate in summer and autumn, when their “storage growth strategy” allows the exploitation of discontinuous upwelling of nutrients. These seasonal changes of dominant species influence the structure of the food web.

Regional climate and patterns of phytoplankton annual succession in the open waters of the Black Sea

The annual succession of phytoplankton of the open waters of the Black Sea was investigated on the basis of a database covering the 30-year period from 1985 to 2014. Seasonal variations of the taxonomic composition were analysed with regard to weather conditions and the physical and chemical properties of the environment. Two different patterns of annual phytoplankton succession were revealed for the post-winter period from March to November. After cold winters a classical annual succession of diatoms → dinoflagellates → coccolithophores → dinoflagellates → diatoms was observed, whereas after regular winters another type of succession; dinoflagellates → dinoflagellates → coccolithophores → diatoms → diatoms, took place. These two successions corresponded to seasonal dynamics of nitrate concentration and its share in the total inorganic nitrogen. During cold years these parameters decreased from spring to summer with a subsequent increase in autumn, whereas in regular years they were unusually high in summer. The enigma of this summer nitrate enrichment is well explained by the hypothesis of increasing cross-shelf nutrient transport. During regular years, weak hydrodynamic forcing occurs throughout the year, resulting in a large number of mesoscale eddies along the shelf in summer–autumn that in turn cause the intense transport of coastal waters rich in nitrate to the Sea interior. Development of the large-celled diatom Pseudosolenia calcar-avis in the sea basin observed in summer is in line with this hypothesis. This mechanism was also confirmed by positive relationships between the high sea-surface temperature, and the low Ekman pumping velocity and mean kinetic energy of currents in winter on the one hand, and the contribution of diatoms to the total phytoplankton biomass in summer–autumn, on the other. A case study of mesoscale eddies in the open waters in summer–autumn demonstrated a shift in species composition to large-celled diatoms inside these structures. Climate warming observed during the last 25 years resulted in a decrease in the frequency of cold winters from 30% to 15%, which has led to a decline in the annual phytoplankton standing stock. Thus, in the Black Sea, climate warming affects phytoplankton not directly by an increase in temperature, but by a decrease in the frequency of cold winters.

The invasive diatom Pseudosolenia calcar-avis and specific C25 isoprenoid lipids as a sedimentary time marker in the Black Sea

The invasive diatom Pseudosolenia calcar-avis and specific C25 isoprenoid lipids as a sedimentary time marker in the Black Sea

C25 highly branched isoprenoid alkenes in the Baltic Sea produced by the marine planktonic diatom Pseudosolenia calcar-avis

C25 and C30 highly branched isoprenoid (HBI) alkenes are lipid biomarkers produced exclusively by certain diatoms and found in sediments worldwide. Here, for the first time, it is shown that the marine planktonic diatom Pseudosolenia calcar-avis (Schultze) (Sundström, B.G., 1986. The Marine Diatom Genus Rhizosolenia (A New Approach to the Taxonomy) (Ph.D. thesis). Lund University, Lund), isolated from near surface waters in Mecklenburg Bay (southwestern Baltic Sea) biosynthesizes one C25:2 and two C25:3 HBI alkenes previously reported in some benthic diatoms. The presence of the same C25 HBI alkenes in surface sediments from Mecklenburg Bay and the Arkona Sea, as well as their co-occurrence with remnant frustules of P. calcar-avis in a sediment core from the northern Baltic Sea, indicates that these lipids are very likely specific biomarkers for this diatom in this region at least. Further, since P. calcar-avis has a tolerance for low salinities (8–10), we also suggest that the occurrence of some of the HBIs produced by this diatom might represent a useful proxy for measuring past changes in inflowing water from the North Sea. The same C25 HBIs, previously found in sediments from the Caspian Sea and the Black Sea, may also be produced by P. calcar-avis in such settings.

Phytoplankton variability in relation to some environmental factors in the eastern coast of Suez Gulf, Egypt.

Water samples were seasonally collected from 12 stations of the eastern coast of Suez Gulf during autumn of 2012 and winter, spring, and summer of 2013 in order to investigate phytoplankton community structure in relation to some physicochemical parameters. The study area harbored a diversified phytoplankton community (138 species), belonging to 67 genera. Four algal groups were represented and classified as Bacillariophyceae (90 species), Dinophyceae (28 species), Cyanophyceae (16 species), and Chlorophyceae (4 species). The results indicated a relative high occurrence of some species namely.; Pleurotaenium trabecula of green algae; Chaetoceros lorenzianus, Proboscia alata var. gracillima, Pseudosolenia calcar-avis, and Pseudo-nitzschia pungens of diatoms; Trichodesmium erythraeum and Pseudoanabaena limnetica of cyanophytes. Most of other algal species were fairly distributed at the selected stations of the study area. The total abundance of phytoplankton was relatively low (average of 2989 unit/L) in the eastern coast of Suez Gulf, as compared its western coast and the northern part of the Red Sea. The diversity of phytoplankton species was relatively high (2.35–3.82 nats) with an annual average of 3.22 nats in the present study. The results concluded that most of eastern coast of Suez Gulf is still healthy, relatively unpolluted, and oligotrophic area, which is clearly achieved by the low values of dissolved phosphate (0.025–0.3 μM), nitrate (0.18–1.26 μM), and dissolved ammonium (0.81–5.36 μM). Even if the occurrence of potentially harmful algae species was low, the study area should be monitored continuously. The dissolved oxygen ranged between 1.77 and 8.41 mg/L and pH values between 7.6 and 8.41. The multiple regression analysis showed that the dissolved nitrate and pH values were the most effective factors that controlled the seasonal fluctuations of phytoplankton along the eastern coast of Suez Gulf during 2012–2013.

PHYTOPLANKTON OF CASPIAN

Aim. The composition of the species of the phytoplankton in the Russian sector of the Caspian Sea in conditions of transgression, anthropogenic and chemical contamination has been studied. Location. The Russian sector of the Caspian Sea Methods. The phytoplankton samples were collected at the depths of 8 – 50m by the use of the Nansen bathometer and subsequently were fixed in 4% formalin. The office processing was carried out in a box of Nozhotta type, which has the volume of 0.1 ml and the triplicate surface, under the light microscope of Biolam P15. The system of domestic diamotologists was used during the classification of Bacillariaphyta, as for the classification of Dinophyta, the Dodge scheme was applied. Cyanophyta algae were classified according to the system of A.A. Elenkina with the amendments adopted by A.I. Proshkin-Lavrenko and V.V. Makarova. The classification of the Chlorophyta division has been done according to the Smith system. Results, main conclusions. Presented the taxonomic structure and the lists of species of the phytoplankton community in the sea coastal shallow waters Russian sector of the Caspian Sea have been presented. A high floristic diversity and domination of small cell forms are characteristics of the modern structure of the coastal shoal waters of the Dagestan part of the Caspian Sea. The auttaclimatizant of 1934, Pseudosolenia calcaravis, has not been discovered in the plankton of the researched water area. The phytoplankton community has been represented by 58 species of six groups: Cyanophyta, Bacillariaphyta, Dinophyta, Euglenophyta, Chlorophyta and the small flagellate. Bacillariaphyta were the basis of both the taxonomic diversity and the biomass. Cyanophita prevailed in number.